Cooling system



Dec. 1, 1964 w. H. NEBGEN 3,159,003

COOLING SYSTEM Filed April 8, 1963 WILLIAM H. NEBGEN INVENTOR.

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AGENT 3,15%,ud8 Patented Dec. 1, 1964 3,159,968 COOLING SYSTEM Wiiiiam H. Nehgen, Woodside, N.Y., assignor to Chemieal Construction Corporation, New York, N.Y., a corporation of Delaware Filed Apr. 8, 1963, Ser. No. 271,319

I 11 Claims. (Cl. 62-98) This invention relates to an improved cooling system for the cooling of fluids by heat exchange with a volatile refrigerant. A new sequence'is provided which permits the effective cooling of a fluid using both the sensible heat and the latent heat of vaporization of the refrigerant. The system of the present invention is most suitably applicable in combination with multi-stage gas compression to provide interstage cooling. In this combination, a substantial reduction in total gas compression horsepower requirement is achieved.

Numerous variations on the basic refrigeration cycle have been proposed in the prior art. Typical of these are the systems disclosed in US. Patents 2,156,096; 2,225,491 and 2,389,106. In these and other similar types of refrigeration systems, the basic means of achieving a cooling effect is through vaporization of a volatile refrigerant while in heat exchange with the fluid being cooled. The resulting refrigerant vapor ,is compressed, cooled and condensed, and recycled as liquid refrigerant. In some cases, sub-cooling of the liquid refrigerant may take place, so that part of the heat load is carried as sensible heat, in warming up the liquid refrigerant to vaporization temperature. However, such heat transfer via heating of the liquid refrigerant prior to vaporization forms in most cases only a very minor proportion of the total cooling effect.

In the present invention, an apparatus arrangement of a refrigeration system and a refrigeration method are provided, which accomplish substantial sub-cooling of the liquid refrigerant and thus permitremoval of a substantial portion of the heat load as sensible heat of liquid refrigerant. The sub-cooled liquid refrigerant is passed in heat exchange with the fluid being cooled, and the liquid refrigerant is thus warmed and partially vaporized. The mixed vapor-liquid stream is withdrawn from the heat exchange unit, and is separated into vapor and liquid components. The vapor component is combined with a recycle vapor stream derived from flash cooling, and the combined vapor stream is cooled and condensed to liquid refrigerant. This liquid stream is combined with the liquid component derived from the heat exchange unit. The combined liquid stream is passed through an expanrequirement is obtained. In this case, the compression power required at each stage of compression is substantially reduced due to the fact that the inlet temperature of the gas stream to each stage of compression is lowered by refrigerant cooling, While the total added power requirement for recycle of vapor and liquid refrigerant components from the flash cooling stage is quite small in comparison to the reduction in gas compression power requirement.

It is an object of the present invention to provide an improved cooling system using a volatile liquid refrigby separate decompression and flash cooling of the liquid sion valve to a lower pressure level, and a flash cooling effect is obtained which cools the liquid refrigerant. The expansion also produces a vapor stream, which is compressed and recycled for combination with the vapor component derived from the heat exchange unit as discussed supra. The cooled liquid refrigerant is pumped up to normal pressure, thus becoming sub-cooled at the pump discharge pressure, and is recycled to the heat exchange unit. 7

The cooling system of the present invention has outstanding advantages. Thus, it has been proposed that a fluid may be cooled in two stages, using cooling water for partial cooling in a first heat exchanger and volatile liquid refrigerant for final cooling in a second heat exchanger. In the system of "the present invention, the entire cooling load may be carried by the single heat exchanger unit, with a net saving in total heat exchanger surface required. In addition, when the system of the present invention is applied to interstage cooling of a gas stream between stages of compression, it has been found that a substantial reduction in total compression power refrigerant. 1

Still another object is to provide a cooling system in combination with a plurality of stages of gas compression, such that interstage cooling is accomplished with reduced net compression power requirements.

These and other objects and advantages of the present invention will become evident from the description which follows. Referring to the figure, a generalized flow diagram of the apparatus arrangement and system of the present invention is presented, as applied to the cooling of a fluid. In the following description, the method and flow diagram will be described in relation to use of ammonia as the volatile liquid refrigerant. It will be appreciated that other volatile liquid refrigerants, such as freon, propane and butane may be employed in the present invention instead of ammonia.

The sub-cooled liquid ammonia stream 1, typically at a pressure in the range of 250 p.s.i.g. to 300 p.s.i.g. and temperature of 0 F. to 32 F., is passed into heat exchange unit 2. Stream 1 may be at a temperature of 32 F. or slightly higher in cases where the fluid being cooled contains water vapor, so as to avoid depositionof solid ice in the heat exchange unit. Depending on the properties of the fluid being cooled, other temperature levels for stream 1 may be provided. It will thus be evident that the ranges of pressure and temperature recited supra for stream 1 are merely typical or preferable, and are not to be construed as restrictive on the scope of the present invention. Similar considerations apply with respect to operating ranges of temperature and pressure recited infra.

Stream 1 passes through the coil 3 of heat exchanger unit 2, and is heated to a temperature typically in the range of F. to F. Vaporization of a portion of the liquid ammonia also occurs. The fluid to be cooled is passed via 4 into unit 2, and is cooled by heat exchange with the ammonia, leaving unit 2 via 5 at a desired lower temperature. In a preferred embodiment, stream 4- is derived from co. ipression stage 25 of a gas compressor, and stream 5 is passed to the next higher compression stage 26 of the gas compressor.

The warmed and partially vaporized ammonia stream leaves coil 3 via 6, and passes into gas-liquid separator unit 7, which may be of cyclonic configuration. Other suitable designs for unit 7 including interior baflles may be provided, to accomplish the division of stream 6 into vapor and liquid components. The vapor component is withdrawn from unit 7 via 8, and stream 8 is combined with recycle. vapor stream 9, which is derived from the flash cooling state of the system in a manner to be de- J scribed infra. The combined vapor stream now passes into vapor condenser 11, in which the vapor is condensed to liquid ammonia. Cooling water or other cooling medium is passed via 12 to the cooling coil 13 of unit 11, and warmed cooling water is withdrawn via 14.

The resulting condensed liquid ammoni is Wi r via 15, from unit 11, typically at a temperature in the range of 70 F. to 190 F. Stream 15 is now combined with the residual liquid ammonia stream 16. withdrawn from the separator 7, to form combined liquid ammonia stream 17. The liquid ammonia stream is now cooled by expansion and decompression to a reduced pressure level. Thus,

stream 17 is passed through expansion valve 18, and is discharged via, 16:, passing directly into flash cooler iii in which a reduce press r l vel typical y in h range f 30 p.s.i.g. to 62 p.s.i.g. is maintained. Flash cooler 20 is a suitable vessel in which substantial equilibrium is achieved; between the flashing ammonia vapor and residual liquid, such that a reduced equilibrium temperature in the range of 0 F, to 32 F. is attained due to. the spontaneous evolution of ammonia vapor at the reduced pressure.

The evolved ammonia vapor is withdrawn from unit 2% via 21, and is compressed by compressor 22; to a. Pressure level suitable for recycle and in the range of about 250 p.s.i.g. to 300 p.s.i.g. The compressed Vapor is discharged from unit 22 via 9, and is recycled in a manner described supra.

The cooled liquid portion is withdrawn from unit 20 via 23. at a temperature in, the range of 0 F. to 32 F., and is pressurized by pump 24 tothe required pressure level for recycle, in the range of 2 50 p.s,i.g. to 300 p. s.i.g. The pressurized sub-cooled liquid ammonia stream is then recycled via 1 for further service as a coolant in the heat exchange unit 2 as described supra.

Numerous variations within the scope of the, present invention will occur to those skilled in the art. Thus, for example, the various processing units, have been illustrated only n a, schematic manner. In actual practice, apparatus units of diifen'ng design may be employed to carryout the functions of the respective apparatus elements illustrated in the flow diagram.

Example An example of; an industrial application of the present invention with its concomitant advantages, will now be described. The apparatus system and, cooling: method of the present invention was applied to the interstage cooling of ammonia synthesis; gas between three stages of compression from an inlet pressure of 204 p.s.i.g, to a final discharge pressure of 5.1 00 p.s.i.g. Compression discharge temperature of the gas was 230. F. at each stage, and the gas stream was cooled to 40 F. in accordance with the present invention, prior to further compression. The ammonia coolant was admitted to the heat exchange unit at 2l F., and a mixed vapor-liquid stream of ammonia was recovered at 110 F.

It was determined that the total compression load was reduced by 1,100 horsepower for a plant handling 3462 m-ols/hour of dry synthesis gas, clue to reductionin the interstage volume of the synthesis gas which was achieved by the cooling system of the present invention. The power required for compression of recycle ammonia vapor and pumping of subcooled liquid ammonia was only of the power saving achieved due tov reduction in the loadingof the main gas compressor. In addition, the, total heat exchange surface required was only 90% of that required in previous systems, where cooling was accomplished in a conventional manner using cooling water and vaporizing ammonia in two stages of cooling. Finally, the net interstage gas pressure drop was reduced by25 psi. due to the fact that the process synthesis gas was passed through one heat exchanger rather than the two units required in prior practice.

What I claim is:

1. In a cooling system, the combination of a cooler for heat exchange between afiuid being cooled and a subcooled volatile liquid refrigerant at elevated pressure, wherein said liquid refrigerant is heated and partly vaporized at said elevated pressure, a separator for division of heated refrigerant into vapor and residual liquid phases, means to pass said heated refrigerant from said cooler to said separator, a condenser for conversion of the refrigerant vapor phase combined with a vaporized refrigerant portion to liquid without compression, means to pass said refrigerant vapor phase and said vaporized refrigerant portion to said condenser, means to combine liquefied refrigerant from said condenser with said residual liquid phase derived from said separator, an expansion valve for cooling of said combined liquid refrigerant by expansion to reduced pressure, whereby a portion of said li uid refrigerant is vaporized, means to. pass said combined liquid refrigerant through said expansion valve, a flash cooler for cooling of liquid refrigerant by said expansion to reduced pressure and separation of cooled vapor and liquid phases, means to pass refrigerant vapor-liquid mixture to said flash cooler from said expansion valve, a vapor compressor for compression of the cooled vapor portion from said flash cooler, whereby said vaporized refrigerant portion is produced, a pump for pressurizing and return of sub-cooled liquid refrigerant to said eooler, and means topass the cooled liquid portion from said flash cooler to said pump.

2. Cooling system of claim 1, in which said condenser for conversion of the, refrigerant vapor phase combined with a vaporized refrigerant portion to liquid without compression is a, water cooled condenser.

Method: of cooling a fluid with a volatile liquid retrigerant which comp i o l ng flu d y heat; exchange with sub-cooled liquid refrigerant at elevated pressure, thereby heating said refrigerant to a higher temperature and forming separate vapor and liquid phases at said ele vated pressure, combining the vapor phase with a stream of compressed vaporized refrigerant at said elevated pressure cooling the combined vapor stream at said elevated pressure. to form condensed liquid refrigerant without compr ssion, c mb ing sa d; n e d l q id refrigerant wi h sai liquid phase. expa d n he m e liq stream to reduced pr sure whe e y a p r n of said liquid stream is vaporized and a cooling etfect is obtained, compressing the vaporized portion of refrigerant, recycling the compressed vaporized portion of refrigerant t s s ep of comb ning w th e ene pb e s said stream of compressed vaporized refrigerant, pressurizing t e co led liqu d tr am w -lerebv s id qui stream is u cooled, and recycling said; sub-cooled liquid stream to. said fluid cooling step. as said sub-cooled liquid refrigerant.

4. Method of claim 3, in which said volatile liquid re ger nt is mm i 5 Method of; claim 3, in which said volatileliquid refrigerant is Freon.

6 Method of 3, in which said volatile liquid etr se st s p pane,

' 7. Method of claim 3, etr ge ant bu a e- 8. Method of claim 3, in which said combined vapor stream is cooled to form condensed liquid refrigerant y he e c an e th iq i a e i 9. Method of cooling 1a fluid with ammonia which comprises cooling a fluid byheat exchange with sub-cooled liquid ammonia, said liquid ammonia being at an elevated pressure in the range of 250 p.s.i.g-. to 3.09 p.s.i.g. and temperature in the range of 0 F. to 32 F., whereby said liquid ammonia is. heated to a temperature in the range of F. to F, and a separate ammonia vapor phase is formed at said elevated pressure, combining the ammonia vapor phase with a compressed recycle stream of ammonia vapor, cooling the combined vapor stream at said elevated pressure to form condensed liquid ammonia without compression at a temperature in the range of 70 F. to 100 F., combining said condensed in which said volatile liquid liquid ammonia at said elevated pressure with the unvaporized liquid ammonia component remaining after said fluid cooling step, expanding the combined liquid ammonia stream from said elevated pressure to a reduced pressure in the range of 30 p.s.i.g. to 62 p.s.i.g. whereby a portion of said liquid ammonia stream is vaporized and the ammonia temperature is reduced to the range of 0 F. to 32 F., compressing the vaporized portion of ammonia to a pressure in the range of 250 p.s.i.g. to 300 p.s.i.g. recycling the compressed ammonia vapor stream to said cooling step as said recycle stream of ammonia vapor, pressurizing the cooled liquid ammonia to an elevated pressure in the range of 250 p.s.i.g. to 300 p.s.i.g., whereby said liquid ammonia is sub-cooled and recycling the subcooled liquid ammonia to said fluid cooling step.

10. Method of interstage cooling in gas compression in a plurality of stages which comprises compressing a gas stream to an intermediate pressure level, cooling the partially compressed gas stream by heat exchange with a sub-cooled volatile liquid refrigerant which is at an ele vated pressure, further compressing the cooled gas stream in the next stage of compression, heating said volatile liquid refrigerant to a higher temperature level at said elevated pressure by said heat exchange with formation of separate vapor and liquid phases, combining the vapor phase at said elevated pressure with a stream of compressed vaporized refrigerant, cooling the combined vapor stream to form condensed liquid refrigerant without compression, combining said condensed liquid refrigerant with said liquid phase, expanding the combined liquid stream to reduced pressure whereby a portion of said liquid stream is vaporized and a cooling effect is obtained, compressing the vaporized portion of refrigerant, recycling the compressed vaporized portion of refrigerant to said step of combining with the vapor phase as said stream of compressed vaporized refrigerant, pressurizing the cooled liquid stream whereby said liquid stream is subcooled, and recycling said sub-cooled liquid stream to said heat exchange step as said sub-cooled volatile liquid refrigerant.

11. Method of claim 10, in which said gas stream' is ammonia synthesis gas and said volatile liquid refrigerant is ammonia.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A COOLING SYSTEM, THE COMBINATION OF A COOLER FOR HEAT EXCHANGE BETWEEN A FLUID BEING COOLED AND A SUBCOOLED VOLATILE LIQUID REFRIGERANT AT ELEVATED PRESSURE, WHEREIN SAID LIQUID REFRIGERANT IS HEATED AND PARTLY VAPORIZED AT SAID ELEVATED PRESSURE, A SEPARATOR FOR DIVISION OF HEATED REFRIGERANT INTO VAPOR AN RESIDUAL LIQUID PHASES, MEANS TO PASS SAID HEATED REFRIGERANT FROM SAID COOLER TO SAID SEPARATOR, A CONDENSER FOR CONVERSION OF THE REFRIGERANT VAPOR PHASE COMBINED WITH A VAPORIZED REFRIGERANT PORTION TO LIQUID WITHOUT COMPRESSION, MEANS TO PASS SAID REFRIGERANT VAPOR PHASE AND SAID VAPORIZED REFRIGERANT PORTION TO SAID CONDENSER, MEANS TO COMBINE LIQUEFIED REFRIGERANT FROM SAID CONDENSER WITH SAID RESIDUAL LIQUID PHASE DERIVED FROM SAID SEPARATOR, AN EXPANSION VALVE FOR COOLING OF SAID COMBINED LIQUID REFRIGERANT BY EXPANSION TO REDUCED PRESSURE, WHEREBY A PORTION OF SAID LIQUID REFRIGERANT IS VAPORIZED, MEANS TO PASS SAID COMBINED LIQUID REFRIGERANT THROUGH SAID EXPANSION VALVE, A FLASH COOLER FOR COOLING OF LIQUID REFRIGERANT BY SAID EXPANSION TO REDUCED PRESSURE AND SEPARATION OF COOLED VAPOR AND LIQUID PHASES, MEANS TO PASS REFRIGERANT VAPOR-LIQUID MIXTURE TO SAID FLASH COOLER FROM SAID EXPANSION VALVE, A VAPOR COMPRESSOR FOR COMPRESSION OF THE COOLED VAPOR PORTION FROM SAID FLASH COOLER, WHEREBY SAID VAPORIZED REFRIGERANT PORTION IS PRODUCED, A PUMP FOR PRESSURIZING AND RETURN OF SUB-COOLED LIQUID REFRIGERNAT TO SAID COOLER, AND MEANS TO PASS THE COOLED LIQUID PORTION FROM SAID FLASH COOLER TO SAID PUMP. 